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© 2001 POWERVAR, Inc.
POWER QUALITY FOR
MEDICAL APPLICATIONS
A Simplified Approach to
Understanding Power Quality
Problems and How to Solve
Them.
© 2001 POWERVAR, Inc.
Why is Power So Important?
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Modern technology is a
tool for achieving
productivity and profit.
It’s designed to run on
clean electrical power.
Clean power for
technology is like clean
fuel for cars.
© 2001 POWERVAR, Inc.
Where Do Power Quality
Problems Start?
Disturbances can be generated external
to a facility.
 Disturbances can be generated internal
to a facility.
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© 2001 POWERVAR, Inc.
External Origins
Lightning
 Grid Switching
 Power Factor Correction
 Inductive Load Switching
 Utility Fault Clearing
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© 2001 POWERVAR, Inc.
What Must The Utility
Provide?
Constant Voltage
 All the current needed (breaker limited)
 Protection for people and traditional
loads (lights and motors) through
grounding procedures.

© 2001 POWERVAR, Inc.
Utility Power Profile
170 volts peak
340 volts p-p
170 volts peak
The shaded area is the RMS
voltage value that we refer to
when we speak of 120 volts.
© 2001 POWERVAR, Inc.
Nominal Voltage Definition

According to ANSI C84.1-1977,
“Voltage Ratings For Electric Power
Systems and Equipment (60 Hz)”, . . . . .
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“The actual voltage at which a circuit
operates can vary from the nominal
within a range that permits satisfactory
operation of equipment.”
© 2001 POWERVAR, Inc.
Internal Origins
Internal disturbances are typically more
numerous and destructive.
 They are created by all the various
electrical loads in your facility.
 The disturbance sources are also closer
to sensitive devices which limits the
damping effect of wiring.
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© 2001 POWERVAR, Inc.
Hospital Noise Sources
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MRI-CAT Scan
Centrifuges
Motors
Heating Elements
Generator Sets
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Refrigerators
Fluorescent Lights
Dimmer Switches
Copy Machines
Computers
Large UPS Systems
© 2001 POWERVAR, Inc.
Grounding
Ground exists primarily for safety.
 Safety ground comes from the point in
the power distribution where
transformer neutral is bonded to
ground.
 This is the only code legal ground in a
facility.
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© 2001 POWERVAR, Inc.
Grounding
Use of alternate, supplementary, or
secondary grounds is a code violation
and creates a personnel safety and fire
hazard.
 Such grounding methods may allow
significant touch potential to exist on
the conductive surfaces of “faulted”
equipment.

© 2001 POWERVAR, Inc.
Grounding
Proper grounding is also required to
assure consistently high power quality.
 Supplementary grounding methods
create ground loops which allow
disturbance currents to flow in
unpredictable pathways.
 Safety ground must be clean. It is the
logic reference for the microprocessor.

© 2001 POWERVAR, Inc.
Patient Safety Issues
UL544 (to be replaced in 2005 by
UL2601.1) addresses patient safety.
 The standard for medical and dental
equipment.
 Specifies the allowable amount of
leakage current to ground for both
patient connected and patient vicinity
applications.
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© 2001 POWERVAR, Inc.
Technology’s Evolution

In the beginning,
society’s
information
processing needs
were simple and
could be
accomplished with
relatively simple
electro-mechanical
systems.
© 2001 POWERVAR, Inc.
Evolution (contd.)

As information
needs increased,
more automation of
the process became
necessary. In 1939,
the world’s first
electronic computer
was invented and
built in Ames, Iowa.
Atanasoff-Berry Calculator, Courtesy Iowa State University
© 2001 POWERVAR, Inc.
Evolution (contd.)
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ENIAC
EDVAC
UNIVAC
Mainframes
Super Mini’s
LAN’s
WAN’s
Foreground - 1 meg dram
Background - 1500 bit memory drum
from first digital computer.
© 2001 POWERVAR, Inc.
Evolution (contd.)
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Migration from vacuum tube to integrated
circuit was driven by the need to increase
speed and reduce physical size.
Changing voltage and current requirements
precipitated the introduction of switch mode
power supplies as a means of further
reducing size and cost and increasing power
supply efficiency.
© 2001 POWERVAR, Inc.
Linear Power Supplies
Inefficient 60 Hz. front end transformer
 Large and expensive
 Provided electrical isolation for the
system electronics
 Narrow regulation range required
compliance with tight input voltage
specifications.
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© 2001 POWERVAR, Inc.
Switch Mode Power Supplies
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High current capability
Reduced size, weight, and cost
PWM circuitry improves efficiency and
provides immunity to voltage variations
Size reduction accomplished in part by
elimination of 60 Hz. transformer. Loss of
isolation negatively impacts performance.
© 2001 POWERVAR, Inc.
Linear
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vs.
Good Isolation
Low Efficiency
Susceptible to
Voltage regulation
issues
Large
Heavy
Expensive
SMPS
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Poor Isolation
High Efficiency
Immune to Voltage
regulation issues
Small and Compact
Lightweight
Inexpensive
© 2001 POWERVAR, Inc.
GENERIC POWER
PROBLEMS
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Blackouts
Brownouts
Sags
Surges
Impulses
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Frequency Changes
Noise
Harmonics
Power Factor
Problems
© 2001 POWERVAR, Inc.
THE BLACKOUT
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A total loss of
power for an
extended period of
time.
Blackouts are easy
to identify for most
of us since we find
ourselves
completely in the
dark.
© 2001 POWERVAR, Inc.
THE BROWNOUT
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Brownouts are a
reduction in overall
line voltage that
may last for minutes
or hours.
They often occur
when demand
exceeds the power
company’s
generating capacity.
© 2001 POWERVAR, Inc.
THE SAG
Sags occur when
line voltage
decreases
momentarily and
then returns to
normal. Sags
generally last
fractions of a
second.
© 2001 POWERVAR, Inc.
Swells
Swells occur when
the line voltage
increases
momentarily and
then returns to
normal. Swells
usually last fractions
of a second.
© 2001 POWERVAR, Inc.
IMPULSES (surges)
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Short Duration
High energy
Often called spikes,
transients, and
voltage surges
They can be
destructive
© 2001 POWERVAR, Inc.
NOISE
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Noise is typically
described as a low
voltage but high
frequency event. It
can readily couple
throughout logic
circuits and be
misread as
legitimate logic
signals.
© 2001 POWERVAR, Inc.
FREQUENCY CHANGES
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Frequency changes
occur on generators, but
under some conditions
can result from utility
operation.
They represent cycle to
cycle changes from the
fundamental 60 or 50
Hz. supply.
© 2001 POWERVAR, Inc.
HARMONICS
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Harmonics are of two types: voltage
harmonics and current harmonics
They occur most often as a result of large
numbers of non-linear loads such as
computer power supplies, etc.
Harmonics are primarily a concern because
they cause overheating of transformers and in
cases have been known to melt wiring.
© 2001 POWERVAR, Inc.
POWER FACTOR
PROBLEMS
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Power Factor ( PF) is an expression of the
phase angle between voltage and current.
In facilities with large numbers of inductive
and non-linear loads, the power factor may
be very low (.65)
The utility company prefers higher PF to
make their system more efficient and cost
effective. PF penalties may be levied.
© 2001 POWERVAR, Inc.
FINDING SOLUTIONS
Electrical disturbances are nothing
more than electrical power in an
unusable or undesirable form.
 All electrical power, both usable and
the unusable kind, obeys certain
physical laws.
 These laws were defined by physicists
Ohm, Kirchoff, and others.
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© 2001 POWERVAR, Inc.
NON-PHYSICAL LAWS
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Certain non-physical laws also govern the
process of eliminating power disturbances.
They are known as Common Sense Laws
Together with the physical laws, they form
the basis for successfully dealing with a
complete range of power problems.
© 2001 POWERVAR, Inc.
Common Sense Law #1
You Can’t Change the Laws of Physics
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Solving power problems requires an
acceptance of physical laws and how
they affect the behavior of power
disturbances. To solve a power
problem, you must use a device that is
capable of affecting the behavior of the
power disturbance in the desired way.
© 2001 POWERVAR, Inc.
Corollary #1
You can’t stop
a charging
elephant by
taking away
his credit card
!!!!!
© 2001 POWERVAR, Inc.
COMMON SENSE RULE #2
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Solving power problems is a process
that requires attention to both results
and investment. It is usually not
possible to get a lot and spend a little.
© 2001 POWERVAR, Inc.
Corollary #2
The Result of Poor Planning
It’s very easy
to spend a lot
and end up
with nothing !!
© 2001 POWERVAR, Inc.
COMMON SENSE RULE #3
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That which is not done right the first
time will almost certainly have to be
done again.
© 2001 POWERVAR, Inc.
Corollary #3
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It’s usually far less
stressful to do
something right
than to be screamed
at later when
someone finds out
you did it wrong!!
© 2001 POWERVAR, Inc.
Effects of Power Problems
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Destructive
disturbances are
powerful enough to
destroy electronic
components.
© 2001 POWERVAR, Inc.
Effects of Power Problems
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Degrading electrical
disturbances do not
cause outright
destruction. They
damage systems in a
way that is invisible.
Many times you will
not learn of the
damage until it is
too late.
© 2001 POWERVAR, Inc.
Effects of Power Problems
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Disruptive electrical
disturbances are low
energy events that
cause data loss,
system lockups, and
aborted tests.
Disruptive power
problems can make
systems very user
“unfriendly”.
© 2001 POWERVAR, Inc.
What Devices Are Used To
Solve Power Problems. How
Do I Decide Which Device Is
The Appropriate One To
Use?
© 2001 POWERVAR, Inc.
The ABC’s
Output
AC
Input
AC
A
Surge
Diverter
B
C
Low
Impedance
Isolation
Transformer
Noise
Filter
D
Voltage
Regulator
E
Battery
Backup
System
F
Frequency
Regulator
G
Ground
Loop
Control
The ABC’s of POWER Conditioning®
© 2001 POWERVAR, Inc.
A - THE SURGE DIVERTER
Surge diverters may be metal oxide
varistors (MOV’s), silicon avalanche
diodes (SAD’s) or gas tubes.
 These devices have a thresh-hold above
which they conduct and limit the rising
amplitude of an impulse.
 They reduce destructive disturbances to
degrading and disruptive ones.
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© 2001 POWERVAR, Inc.
SURGE DIVERTERS
Good for control of catastrophic events
 Most will either degrade or be
destroyed by repeated exposure to high
energy power disturbances.
 Surge diverters are generally
inexpensive, but remember they are
only one small part of the power
protection plan.

© 2001 POWERVAR, Inc.
B - THE ISOLATION
TRANSFORMER
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Isolation transformers provide a “code legal”
point for bonding electrical system neutral to
ground.
This N-G bond is the focal point of what FIPS
Pub. 94 refers to as a “newly derived power
source”.
In plain language, isolation transformers
eliminate common mode voltage.
© 2001 POWERVAR, Inc.
ISOLATON
TRANSFORMERS (contd.)
This capability is a very important one
for today’s systems.
 Modern systems require ultra-quiet
ground references to function properly.
 Noisy ground references are the most
common disruptive power problem.
 Isolation transformers are expensive, so
many manufacturers leave them out.

© 2001 POWERVAR, Inc.
THE ELEGANCE OF A
TRANSFORMER
In addition to creating a clean ground
reference, transformers have an often
overlooked benefit.
 The transformer isolates or electrically
separates the system from any other
electrical device in the facility. This
permits better control of the power
flowing to a system.
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© 2001 POWERVAR, Inc.
C - THE POWERLINE
FILTER
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Powerline filters are needed to address the
high frequency, low voltage disturbances that
may be missed by the surge diverter.
These disturbances are often referred to as
conducted disturbances, EMI, RFI, etc.
Powerline filters address degrading
disturbances by diverting them to ground.
© 2001 POWERVAR, Inc.
FILTER INADEQUACIES
This action turns a degrading
disturbance into a disruptive one.
 The electrical characteristics of filters
can often interact with the
characteristics of electrical wiring
producing results that are undesirable
as well as unpredictable.
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© 2001 POWERVAR, Inc.
D - THE VOLTAGE
REGULATOR
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Voltage regulators, as their name implies, are
designed to maintain voltage levels within
specifications.
They may take one of several different forms.
All voltage regulators maintain voltage levels
by controlling the flow of current in a circuit a possible drawback for SMPS.
© 2001 POWERVAR, Inc.
VOLTAGE REGULATOR
TYPES
Dedicated electrical circuits
 Ferro-resonant isolation transformers
(CVT)
 Tap-switching isolation transformers
 Tap-switching autoformers
 Electronic PWM regulators
 Magnetic synthesizers
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© 2001 POWERVAR, Inc.
D - VOLTAGE
REGULATORS
Voltage regulators were often used with
older generation systems where steady
voltage was mandatory.
 Modern systems with switch mode
power supplies are very tolerant of
voltage variations. As a result, voltage
regulators are generally no longer
necessary.
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© 2001 POWERVAR, Inc.
E - THE BATTERY (UPS)
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The battery or UPS
is used to provide
continuity of power.
UPS systems are the
most misunderstood
power protection
device.
They come in a
variety of designs.
© 2001 POWERVAR, Inc.
STANDBY UPS
The battery or reserve power section
does not activate until after utility
power is lost. Transfer from utility to
battery occurs in a few thousandths of a
second.
 Most standby UPS systems provide
only surge diversion and noise
filtration. Isolation is seldom provided.

© 2001 POWERVAR, Inc.
LINE INTERACTIVE UPS
Line interactive UPS systems function
similar to standby UPS.
 Their design includes a voltage
regulating transformer that functions to
permit a wider operating range without
depleting batteries.
 Most include surge diverters and filters
but no isolation transformer.
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© 2001 POWERVAR, Inc.
ON-LINE UPS
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On-line UPS systems are those in which the
inverter is the primary power supply.
There is no transfer time involved when
utility power is lost.
The design provides natural surge diversion
and noise filtration, but many on-line systems
may still lack an isolation transformer.
© 2001 POWERVAR, Inc.
HYBRID UPS
Numerous hybrid designs also exist.
 They may provide varying levels of
protection depending on the
components they include.
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© 2001 POWERVAR, Inc.
E - THE BATTERY (contd.)
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Inverter design also varies tremendously.
Inverter designs include sine wave, modified
sine wave, square wave, and modified square
wave (the last three often resulting in waves
of nausea, waves of despair, and ultimately
the opportunity to wave goodbye to your
expensive system!)
© 2001 POWERVAR, Inc.
E - THE BATTERY (contd.)
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The UPS is the most misunderstood power
protection technology available today.
Correctly selected, the UPS can provide total
and complete power protection.
Improperly selected, hundreds or thousands
of dollars may be spent for little more
protection than that gotten from a surge
diverter.
© 2001 POWERVAR, Inc.
F - THE FREQUENCY
REGULATOR
In the United States, the frequency of
utility power is 60 Hz. In much of the
rest of the world it’s 50 Hz.
 Frequency regulators make certain that
utility power stays at the right
frequency.
 This is important for things like motors
and transformers.
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© 2001 POWERVAR, Inc.
G – GROUND LOOP
CONTROL
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Ground loops exist anytime components are
networked together and powered from
separate sources (i.e. branch circuits, panels,
transformers, etc.)
Differences in the circuit characteristics cause
“loop currents” to flow through the
interconnecting data cabling, which leads to
system disruption
© 2001 POWERVAR, Inc.
G – GROUND LOOP
CONTROL
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Networked systems in the medical
environment are as susceptible to the
problems caused by ground loops as any
other networked system
When used as part of the total protection
formula, special power conditioning elements
called Ground Guard™ can prevent ground
loops from forming.
Ground Guard eliminates the requirement for
dedicated/isolated electrical wiring
© 2001 POWERVAR, Inc.
What Solutions Are
Appropriate For Today’s
Sophisticated Technology?
© 2001 POWERVAR, Inc.
What Symptoms Are Signs
That Our Systems Are Being
Affected By Power Quality
Problems?
© 2001 POWERVAR, Inc.
Today every system needs:
A - A Surge Diverter
 B - An Isolation Transformer
 C - A Powerline Noise Filter
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These are the minimum requirements.
If data, software, or memory contents
are volatile a UPS may be required as
well.
© 2001 POWERVAR, Inc.
What About UPS’s?
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UPS systems may be either standby, line
interactive, or on-line. Systems with modern
power supplies (SMPS) don’t really care
which one you use.
UPS Systems should provide a SINEWAVE
output from the inverter.
UPS Systems MUST INCLUDE a surge
diverter, filter, and isolation transformer.
© 2001 POWERVAR, Inc.
What are the Symptoms?
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Damaged hardware
Erratic operation
Halted tests
Communication
errors
Unreliable test data
Unexplainable
problems
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Slow system
operation
Numerous service
calls
System lockups
Damaged or lost
data or software
Problems that
cannot be
duplicated
© 2001 POWERVAR, Inc.
What Are The Costs?
Power disturbances account for 14-21%
of total service costs.
 LAN’s function properly 94% of the
time. The other 6% of the time, they
cost corporations an average of $3.48
million in losses per year.
 Power problems are the number one
cause of computer damage.

BMI Study
Infonectics, Inc.
David Johnson, CEO,
Safeware, Inc.
© 2001 POWERVAR, Inc.
What Can Proper Power
Conditioning Provide?
Better system performance
 Fewer communication errors
 More reliable data
 Fewer service calls
 Increased production time
 Lower cost of ownership
 Higher revenue generation

© 2001 POWERVAR, Inc.
Properly specified and
installed, power quality
solutions will increase
productivity, improve patient
care, and pay for themselves
through reduced operating
and maintenance costs.
© 2001 POWERVAR, Inc.
© 2001 POWERVAR, Inc.